Antibiotic and mercury resistance in the cultivable oral microbiota of children
The commensal microbiota of the oral cavity may act as a reservoir of antibiotic- resistant microorganisms, and factors which may promote this antibiotic resistance need to be determined. The aims of this PhD were to determine the prevalence and proportion of antibiotic-resistant bacteria in the cultivable oral microbiota isolated from the dental plaque of healthy children and to investigate factors which may promote antibiotic resistance. Such factors may include, previous antibiotic use, ethnicity and cross resistance with heavy metal resistance genes. To investigate tetracycline-resistant oral bacteria more fully, the effect this antibiotic has on the antibiotic resistance profile and microbial community of microcosm dental plaques was investigated using an in vitro system. The ability of a tetracycline resistance determinant to transfer within an oral biofilm was also determined. Dental plaque from children aged 4-5 years old was screened for the presence of antibiotic- and mercury-resistant bacteria. The majority of the children harboured a diverse collection of ampicillin-, penicillin-, erythromycin-, and tetracycline-resistant bacteria. None of the children harboured metronidazole- resistant anaerobic bacteria or Gram-positive vancomycin-resistant bacteria. Amoxicillin use in the previous three months increased the number, proportions, MICs and cross-resistance profile of the ampicillin-resistant isolates. The percentage of tetracycline-resistant bacteria was greater in South Asian and Japanese children than in white children, suggesting possible ethnic differences in the levels of tetracycline-resistant oral bacteria. 71% of the children harboured mercury-resistant oral bacteria and the median percentage of the total oral microbiota resistant to mercuric chloride was 0.007% (range 0-5.3%). 60% of the mercury-resistant isolates were also resistant to at least one of the four antibiotics tested. Using a model system it was shown that the addition of tetracycline to microcosm dental plaques altered the composition and enriched for antibiotic-resistant bacteria to tetracycline and other unrelated agents. Tetracycline resistance was shown to transfer in a model oral system. It is hoped that this work will help in evaluating factors which promote antibiotic resistance in the oral cavity of children.